Stocks fell on Wednesday after President Donald Trump taunted Russia on Twitter to "get ready" for a possible missile strike on Syria.
The Dow Jones industrial average closed 218.55 points lower at 24,189.45 as Boeing fell 2.2 percent. The S&P 500 declined 0.6 percent to 2,642.19, with telecommunications and financials dropping more than 1 percent each. The Nasdaq composite dropped 0.4 percent to close at 7,069.03.
Trump said in a tweet: "Russia vows to shoot down any and all missiles fired at Syria. Get ready Russia, because they will be coming, nice and new and 'smart!' You shouldn't be partners with a Gas Killing Animal who kills his people and enjoys it!"
Banks helped lead the decline. Shares of Citigroup, Morgan Stanley and Goldman Sachs all closed lower.
Safe havens like gold and U.S. Treasurys rose on the news. Crude oil prices also spiked higher.
"It's not that this wasn't expected. Trump had already hinted at a response," said Quincy Krosby, chief market strategist at Prudential Financial. "I think the market was caught off-guard by the tone of the response."
Earlier, the S&P 500 and Nasdaq erased their losses, while the Dow traded well off its lows.
The president's threat comes after Russia's ambassador to Lebanon told local media that Russia would shoot down American missiles headed Syria's way. This follows an alleged chemical weapons attack by President Bashar Assad that killed dozens in a rebel-held area over the weekend.